Figure 2:

Effect of anesthesia on single unit firing. The firing rates of all recorded single units are shown for isoflurane (a) and sevoflurane (b), corresponding to the last minute of each phase before, during and after anesthesia. Cells are arranged from lowest to highest firing rate. Interneurons are marked with a black circle on the top of the figure. The colored lines serve as a visual guide to illustrate the level of activity across all units for each phase. In the awake state prior to anesthesia, both groups show a similar distribution of single unit activity. Neuronal activity decreased for all cells during anesthesia in air and 80% O₂, to a degree that was not necessarily proportional to the initial firing rate. The logarithmic scale shows changes in low-frequency single units in greater detail (c, d). Note that zero values for firing rate were replaced with 0.01 to prevent missing points on the log scale. For each phase of the experiment single unit firing was averaged across all recorded cells for isoflurane (e) and sevoflurane (f) groups. The graph shows the average for all cells as well as average of interneurons (IN) and pyramidal cells (PC) separately. Means were calculated from averaging the firing rates during the last minute of each phase, and were normalized to the pre-anesthesia level. For both drugs, single unit activity decreased significantly and remained at a steady-state level under anesthesia, and then returned to near the pre-anesthesia level within 20 minutes. The decrease in firing under sevoflurane was significantly greater than under isoflurane. There was no significant difference between anesthesia delivery in air or 80% O₂ for either drug, with the exception of an ongoing decrease for PC under sevoflurane. Asterisks indicate significant changes between the awake state and the initial phase of anesthesia, as well as the final phase of anesthesia and recovery.